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"  The devastation wrought by an epic Mississippi River flood nearly a century ago\u2014more than 500 people dead, another 700,000 displaced and 26,000 square miles underwater\u2014inspired Randy Newman to compose the poignant song, Louisiana 1927. And now, as the Mississippi River flirts with levels and flow rates not seen in decades, the U.S. Army Corps of Engineers will try to avoid any kind of encore of that long-ago flood as they rely on an enormous infrastructure system unknown to most Americans outside of southern Louisiana.  The Corps is pulling out the stops of its Mississippi River &amp;amp;amp; Tributaries Project, a sprawling set of levees, revetments, spillways and floodways devised to control a restless river fed by the third-largest watershed in the world. Robert A. Thomas, director of the Center for Environmental Communications at Loyola University in New Orleans, says this federal flood-control plan was enacted after the 1927 catastrophe to protect the river and its communities. &amp;quot;It&amp;#039;s all pretty monumental,&amp;quot; he says. &amp;quot;It was foresight on their part, to look that far down the road. All it took was the 1927 flood.&amp;quot; Now, though, the system is facing its toughest test in decades. Earlier this week, as the Mississippi was cresting in Memphis, Tenn., engineers opened the Bonnet Carre Spillway 30 miles above New Orleans for only the 10th time in its 80-year history. Completed just four years after the devastating 1927 flood, the 1.5-mile-long control structure holds 350 bays, each of which is 20 feet wide and dammed by creosote timbers called &amp;quot;needles&amp;quot; that can be pulled out with cranes. When completely open, 250,000 cubic feet per second (cfs) of water pours into a 6-mile-long floodway flanked by guide levees draining into Lake Pontchartrain, which is on the north side of New Orleans.  By May 12, the Corps had opened 212 bays, and all 350 bays are expected to be open within a few days, according to Louisiana Governor Bobby Jindal. State officials hope this will prevent river volume at New Orleans from exceeding 1.25 million cfs. And another enormous emergency mechanism, the Morganza Control Structure, could soon be activated for the first time in nearly 40 years. On May 7, the commander of the Corps of Engineers&amp;#039; New Orleans District, Col. Ed Fleming, made a request to the Mississippi River Commission to open the gates at Morganza, 35 miles northwest of Baton Rouge. Approval for this action, which would send floodwaters into the Atchafalaya Swamp, is expected by early next week. The Morganza may be needed because the Bonnet Carre alone may not bring enough relief\u2014upstream at Red River Landing, Mississippi River flow rates of 1,449,000 cfs and rising were reported Friday morning. (By comparison, an estimated 2,120,000 cfs raced past at the height of the 1927 flood.) But diverting water to save New Orleans and Baton Rouge would send floodwaters to other parts of Louisiana\u2014particularly near the Atchafalaya, the largest river swamp in North America. The Atchafalaya is a shorter, steeper route to the Gulf of Mexico than the Mississippi&amp;#039;s current meandering path past New Orleans; it empties into the Gulf in southern Louisiana near Morgan City. The Mississippi nearly shifted to this route in April 1973, when the swollen river collapsed a wing wall and scoured deep pits beneath the Low Sill Structure of the Old River Control Complex (ORCC), which was designed to prevent the Atchafalaya from capturing the Mississippi. To alleviate pressure on the ORCC, the Corps opened 42 of the 125 gates at Morganza, a 4000-foot concrete weir that, at that time, hadn&amp;#039;t been used since its completion in 1954. The ORCC held; the Mississippi stayed in its course. After a 38-year hiatus, Morganza&amp;#039;s cranes may once again open some of its huge (28-feet-wide by 22-1/2-feet-tall) steel gates. Current flow rates at Natchez, Miss., exceed 2 million cfs, and the threshold for uncorking Morganza is just 1.5 million cfs. At capacity, the Morganza complex can divert 600,000 cfs into a five-mile-wide floodway. A stilling basin slows down the water to mitigate erosion and then directs the discharge 20 miles southward into the Atchafalaya Basin. &amp;quot;It&amp;#039;s another way to get water out of the system,&amp;quot; said Chris Accardo, chief of operations for the Corps&amp;#039; New Orleans District. &amp;quot;The hydraulic folks will tell us each day which gates to lift so we can maintain 1.5 million cfs at Red River Landing. It varies, based on predictions and flow rate at the time. We don&amp;#039;t open all the gates at one time.&amp;quot; The question is, what about the towns and farmland in the floodway? The adjacent village of Morganza should stay dry, but residents of the Atchafalaya swamp as well as Morgan City and Houma may experience flooding. Morgan City is already reporting high water\u2014the result of the torrent released through the OCRR. Opening of the Morganza Floodway could inundate 3 million acres, including 18,000 acres of crops such as soybeans, cotton, rice and sugarcane, according to the Louisiana Department of Agriculture. The estimated 2500 people living inside the Atchafalaya floodway are preparing for evacuation. According to Gov. Jindal, another 22,500 people may be affected by some flooding. Jim Delahoussaye, a former water-pollution-control biologist and commercial fisherman who lives in Butte La Rose, is one of those preparing to leave. &amp;quot;The Corps is using the Atchafalaya floodway as a giant shunt,&amp;quot; he says. &amp;quot;We knew they could do that.&amp;quot; As he packs up valuables and heirlooms from his house\u2014a 12-year-old replica of a classic Cajun cottage\u2014he says that the water is supposed to crest just 1 foot below the floorboards of his raised home.  &amp;quot;We didn&amp;#039;t buy this property without doing a lot of research into its history and what might happen under different conditions,&amp;quot; Delahoussaye says. &amp;quot;Where we are supposedly has never gone underwater. It did not flood here in 1927. The reason was there were no levees. The water didn&amp;#039;t come up; it spread out. Now levees contain all the flow. It&amp;#039;s just like a bathtub\u2014the water has to come up.&amp;quot; Robert Thomas says that the area has been a federal floodway since the early 1950s. The Corps holds easements on land in the Morganza Floodway, and sends a written notice annually to residents reminding them of its potential operation. But if the Mississippi continues to rise, as predicted, and Morganza remains closed, the consequences would be grim. According to the Corps of Engineers, additional floodwaters could prompt levee failures and inundations from Morganza to the Gulf, including all of New Orleans. Despite the threat to those downstream, Thomas says, there may be no choice but to open the Morganza. Should the ORCC, Bonnet Carre and Morganza be unable to handle all the floodwater, the Corps can still call on one last-ditch emergency structure: the Fuse Plug Levee on the west side of the Atchafalaya. It&amp;#039;s designed to send as much as 250,000 cfs\u2014the same capacity as the Bonnet Carre Spillway\u2014into the back swamp and farmland. The Fuse Plug is the fail-safe in case of a flood even worse than 1927. But, Thomas says, nobody knows how well it would work\u2014it&amp;#039;s never been needed. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/science/environment/a11703/how-it-works-the-spillways-trying-to-control-the-rising-mississippi-5739028/>